31 December 2010

30 December 2010

In the park near our house there is a ledge covered with large limestone rocks situated not too far above a lake. This artificial structure probably has some sort of drainage function into the lake below. However, it is not clear where the water may be coming from. Anyway, what concerns here us is not the hydrology of the park, but the little snails that call the rocks their home. I took these pictures of them yesterday.

The snails were, of course, dormant. As you can see in the picture below, there were both big ones and little ones.

I believe these are a Vallonia species, probably Vallonia costata. However, even the largest snails I saw did not have the typical thickened and reflected lip characteristic of the adults of the genus.

A closer search on a warmer day should turn up more specimens to pinpoint the identity of the snails.

28 December 2010

There are innumerable examples of the use of the shells of marine snails as jewelry, decoration or tools throughout human history. I have written about some examples in this post and this post.

Examples of comparable uses of land snails shells, on the other hand, are harder to come by. That is probably because most land snail shells are less prettier and much thinner, therefore, less durable than marine snail shells.

A note in the January/February 2011 issue of Archaeology mentions a skeleton from around 800 BCE found in Peru that was adorned with about 180 land snail shells. The shells visible in the picture accompanying the article are quite large. The ancient Peruvians were undoubtedly paying attention to at least the larger snails around them.

27 December 2010

The lake near our house has been frozen for about 10 days. During a walk a few days ago, we noticed several tracks crisscrossing the frozen surface of the lake that also had a thin layer of snow on it. But the tracks were not fresh and I could not identify them readily.

At least some of the tracks in the above picture may have been made by white tailed deer. But I don't think the ones in the next picture are deer tracks. The straddle, or the width, of deer tracks are normally very narrow. These tracks may belong to a raccoon or a fox.

Here is another set. This could be a deer track, but it's hard to tell, because the snow had melted and distorted the foot prints.

26 December 2010

This spotted cucumber beetle (Diabrotica undecimpunctata) was in a bag of spinach we bought last week. The spinach had not been frozen, but the beetle was limp and motionless after it was removed from the refrigerator and remained so at room temperature.

According to the bag, the spinach was produced by a Massachusetts company. The spotted cucumber beetle is said to be a widespread species in eastern North America.

22 December 2010

We have all heard the claim that eating vegetables and fruits is good for us and that their consumption may help ward off many illnesses, including cancer. This receives endorsements from all sorts of health organizations and scientists so frequently that it may have reached the state of being a conditional truth. For example, here is a U.S. Government page that says "...those who eat more generous amounts as part of a healthful diet are likely to have reduced risk of chronic diseases, including stroke and perhaps other cardiovascular diseases, and certain cancers".

In reality, preventive nutrition is very much a science of uncertainties. This is so probably because of the enormous among-person variability that exists in any human population that results from the innumerable external and internal factors that control our phenotypes. Another confounding factor is the practical difficulty of monitoring and controlling peoples' diets for research purposes.

Therefore, it should not come as a surprise that a recent review* makes the bold counter claim that there is not much experimental support behind the assertion that eating plenty of fruits and vegetables reduces the risk of getting cancer.

Nutritional principles indicate that healthy diets should include at least moderate amounts of fruit and vegetables, but the available data suggest that general increases in fruit and vegetable intake would not have much effect on cancer rates, at least in well-nourished populations.

The author then goes on to review the supposed associations of specific cancers with fruit and vegetable consumption. We learn the following about prostate cancer:

There has been much interest in the possibility that fruits and vegetables, such as tomatoes, which are rich in the carotenoid lycopene might reduce the risk for prostate cancer, but overall the data do not support this hypothesis...

Having written this, I will now take a break to enjoy a platefull of fruits with a glass of wine. They do taste good and they won't harm me. That's all that matters.

21 December 2010

Here are the series of pictures of the moon I took early this morning during the full lunar eclipse. We were lucky that the sky remained clear throughout the night.

The 1st one shows the pre-eclipse moon at 19:44 on 20 December.

I went to bed before midnight, but got up around 01:15 and stayed up for the next hour and a half. The good thing was that I didn't have to venture far from the house to photograph the moon. Until about 02:00 I had an unobstructed view of it from my deck. Soon after that the moon moved behind a pine tree. But even then I only had to step down into the backyard for a clear view of the moon.

The next shot taken at 01:26 shows a shadow falling across the upper lefthand edge of the moon. The eclipse had started.

At 01:53, the eclipse was obvious.

Most of the moon's face had been shadowed by 02:19. At that time, the stars near the moon had become visible. The eclipsed moon and the bright stars formed a nice spectacle that more than justified standing at below-freezing temperatures outdoors in the middle of the night.

This is the last photo I took at 02:41. These last pictures showing the full eclipse didn't come out good. Over at A DC Birding Blog, John has much better ones.

I took all the pictures with an Olympus E-500 camera using a Zuiko 40-150 mm lens set at 150 mm. Until shortly before the moon was fully eclipsed, I did not need a tripod and could hold the camera in my hands. Even at 02:09 the moon was still bright enough for a shutter speed that did not require the use of a tripod. Once the brightness of the moon was reduced to a sliver, however, I had to reduce the shutter speed and put the camera on a tripod. At the time when the full eclipse started, I was using a shutter speed of 1/30 s at f4.5 and a sensitivity of 400 to be able to capture the red light covering the eclipsed face of the moon. I should also have used a remote release, for some of the last pictures turned out blurry from the shaking of the tripod.

17 December 2010

This is one of the species in the widespread and speciose family Enidae. It is a snail of limestone rocks on the mountains of western Turkey.

I have never seen the snail itself. But I did photograph dormant individuals stuck on rocks in the summer of 2006.

Empty shells of Zebrina cosensis seem to quickly fade into a whitish color. The shell of the live snail in the above photo had a blue tint, while the specimen in the 1st photo, which was collected empty, has retained brownish patches.

14 December 2010

Repeat photography is the photographing of a scene repeatedly over a long period. It is usually applied to wilderness areas to document natural or human-caused changes over many decades. The U.S. Geological Survey has an ongoing repeat photography project involving mainly the deserts in southwest U.S. Some sets of photos from that program may be seen over at Wired.

Long before I learned that repeat photography was a formal procedure, I got interested in it on my own. My so far imprecise contributions may be seen in this post and this post.

To be most useful, a repeat photo of a scene should be taken from the same position and distance. But sometimes I learn of the existence of an older version of a picture I took when it's too late to correct for any differences in the composition. Here is an example.

Last June in Turkey, we visited the ruins of Priene. While we were at the theater, I photographed this goddess sitting in one of the front row seats that must certainly have been reserved for the notable.

Just last night, while skimming thru the Turkish archaeologist Ekrem Akurgal's Ancient civilizations and ruins of Turkey, I saw this picture of the theater of Priene.

They are the same seats photographed from a slightly different point. After going back and forth between the 2 photos several times, we decided that the seat marked with the red X in the Akurgal photo is the one in which the goddess is sitting in mine.

Akurgal's book was 1st published in 1969. The pictures in it may have been taken in the 1960s if not earlier. During the more than 40 years that separates the 2 pictures, the bottom right-hand corner of the goddess's seat broke off. We couldn't spot any other glaring differences between the 2 photos.

12 December 2010

After several days with temperatures just above the freezing and even colder nights, the weather got slightly milder over the weekend and it rained. So this morning I decided to do one more search for slugs in the woods before the cold weather returned.

10 December 2010

The 1st detailed account of the little semi-terrestrial snail Pomatiopsis lapidaria was published by William Stimpson (1832-1872) in 1865. Stimpson's descriptions of the anatomy and behavior of Pomatiopsis lapidaria are surprisingly accurate. For example, he described the snail's eye as follows.

The eye is situated on the outer side of a rather prominent swelling out or protuberance of the head at the base of the tentacle. On the upper and inner side of these protuberances there is a conspicuous longitudinal fusiform spot of flake-white or yellow, which is a prominent character, probably, however, of specific importance only.

When I first read this passage, I was on the train home. I put a note on the margin of the paper to remind myself to check this in my photographs of Pomatiopsis lapidaria. Sure enough, an elongated, yellowish band is clearly visible above each eye in the pictures showing the heads of the snails I photographed.

I don't know what exactly those spots are and what function, if any, they may have. The "pigment layer" lining the eye chamber of Pomatiopsis lapidaria that Dundee (1957) mentioned may have been the same structure. Davis (1967) referred to them as "glandular units".

Here is the entire picture showing the rest of the snail. The whitish oval plate on the snail's foot below the shell is its operculum.

09 December 2010

08 December 2010

Lately, I have been interested in the relative dimensions of snails' feet and shells. What factors influence and control the size of a snail's foot relative to the size of its shell? The shape of the shell seems to matter. I have noticed in tiny species whose shells are longer than they are wide, the length of the foot is close to that of the shell. Here is a Vertigo pygmaea from my backyard.

The white line is equal in length to the snail's foot, while the blue line to its shell. The latter was about 1.9 mm long*. The ratio of the lengths of the blue and white lines (foot/shell) was 0.80.

This previous post was also about this subject and featured another example. Expect more in the future.

06 December 2010

A recent paper* of mine opened with this sentence: "During their daily survival, terrestrial gastropods have two primary requirements they need to fulfill: the intake of adequate food and the maintenance of proper hydration."

In the context of a paper on natural selection that I was reading today, I started thinking about this again. Then I came up with following list of the essential requirements in the life of an animal. They are in no particular order.

Of course, none of these processes are independent of each other. For example, reproduction also requires energy, while the act of searching for and consuming food exposes an animal to biological and physical dangers. Even the food consumed could be, and often is, a source of parasites. This interdepency was something I emphasized briefly in my paper: "Food intake requires that the animals be active, but activity results in water loss as evaporation from the body surfaces and as slime left behind. The surface a gastropod is on must be sufficiently wet, the air humidity adequately high, and its food of a high enough water content so that daily activity doesn’t result in a negative water balance."

The requirement to obtain enough oxygen doesn't seem to be a major concern for terrestrial animals. However, it is indeed a critical requirement for aquatic animals.

Because I work with animals, I normally think in terms of animals. But these requirements are also essential and sufficient for all other forms of life. The requirement #3 must, however, be modified to suit the idiosyncrasies of particular organisms. For example, photosynthetic plants synthesize their own "foods" from sunlight.

Natural selection operates during the fulfillment of each and every one of the 4 requirements.

*Örstan, A. 2010. Activities of four species of land snails at low temperatures. Journal of Conchology 40:245-246. See this post for more on this paper.

05 December 2010

I have written about the little semi-terrestrial snail Pedipes ovalis in this post and this post. A small number of them that I collected in Florida in April 2009 and brought home to Maryland stayed alive for several months and provided me with hours of fun and enlightenment.

The shell aperture of Pedipes ovalis is surrounded by two columellar and one prominent parietal teeth.

A characteristic of the genus is the anatomy of the foot, which is divided by a transverse groove into an anterior propodium and a posterior metapodium.

A casual examination of a specimen preserved in alcohol led me to a hypothesis to explain the function of the long parietal tooth. A short paper detailing my ideas just came out in Basteria, the journal of the Netherlands Malacological Society*.

Unfortunately, Basteria won't let me post the paper on the Web for a year. But if you want a pdf copy, send me an e-mail and I'll happy to send you one.

Here is the abstract from the paper.

When Pedipes ovalis withdraws into its shell, its foot is sequestered between the parietal and the columellar teeth, while the sinus above the parietal tooth encloses the portion of the mantle skirt with the pneumostome. This organization suggests that one function of the long parietal tooth characteristic of the genus is to prevent the snail’s foot from blocking the pneumostome.

03 December 2010

I found this little snail under a log not too far from the Potomac River during last weekend's field trip. It's darker color in comparison to that of Zonitoides arboreus makes me think that it's Zonitoides nitidus, but I may be mistaken. A dissection would help me identify it more definitely, but I left the snail where I'd found it.

In Land Mollusca of North America (1946), Pilsbry wrote that the "animal" of Z. nitidus is black. He probably meant the snail's foot and that is why the shell, especially the body whorl, which is translucent, appears dark. The habitat of my specimen, near the Potomac, fits the habitat of Z. nitidus, which is, also according to Pilsbry, "generally found near water or in marshy places".